Technical Field
The present invention relates to an angle detection device including a plurality of photodetectors and a survey instrument installed with the angle detection device.
Description of Related Art
Survey instruments that detect horizontal angles and vertical angles by using angle detection devices have been known. For example, an angle detection device that detects horizontal angles and vertical angles by using two absolute encoders is taught by Patent Document 1 (Japanese Laid-Open Patent Publication No. 2007-178320). Each of the absolute encoders has two pairs of photoemitters and photodetectors and the photoemitters and the corresponding photodetectors are disposed so as to interpose a scale plate between them (i.e., the photoemitter and the corresponding photodetector form an opposed angle detector). Note that each of the photodetectors has a linear light-receiving area. The pairs of the photoemitters and photodetectors are arranged to be rotatable around the center of the scale plate. Accordingly, each of the absolute encoders of the angle detection device can detect horizontal angles and vertical angles as negating angle detection errors caused by wobbling of the rotary shaft.
Each of the absolute encoders of the conventional angle detection device has a CPU (arithmetic processor) that processes analog signals outputted from each photodetector and measures or calculates the horizontal angle and vertical angle as negating angle detection errors caused by wobbling of the rotary shaft. The conventional angle detection device appropriately amplifies the analog signals by an Analog-Front-End (AFE) and converts the analog signals into digital signals. The digital signals are then outputted to the CPU, and the CPU calculates the horizontal angle and vertical angle based on the digital signals.